Now, China has overtaken Russia, becoming the second country in the world who has two fourth-generation fighter jets in test flight period after the United States.

这标志着中国超过俄罗斯，成为继美国后第二个同时试飞两种四代机的国家。

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The calculation and simulation programs were also developed. The relations between the ground targets' absolute altitude and system parameters in a single flight period were analyzed in detail.

对单个飞行周期内地面目标的绝对高程精度与系统状态参数之间的关系进行了详细分析。

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Controllers entered flight plans manually for all flights that did operate during that period, and the FAA said safety was not affected.

航空管理人员对正在运行的航班采取人工录入的方法处理，航空管理局表示飞行安全并没有受到影响。

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SpaceShipII is expected to take passengers to an altitude of 68.3 miles in just a two-hour flight that includes a four-minute period of weightlessness.

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Just as airlines require passengers to turn off their mobile devices for the duration of the flight, the withdrawal is confined to a limited period.

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My wife and I flew to Argentina in 1995 after a long period when neither of us had taken a long-haul flight for many years.

BBC: News Online